Food Hypersensitivity in Pets

 Food hypersensitivity is an uncommon skin disorder in dogs and cats that is caused by an allergic reaction to food. The component of the food that the animal reacts to is usually a protein source (beef, chicken, egg, cow's milk) but it may be a minor component (preservative, additive, dye). Because this is an acquired disease, the animal has often been fed the food for months to years before the onset of the disease.

The most common sign of food allergy is an intense, nonseasonal itch. In dogs, the itch tends to be generalized, but the ears, face, and feet may be more severely affected. Some dogs may exhibit signs of recurrent ear disease as the only manifestation of food allergy. Food allergy in cats usually affects the face and neck, and the itch may be so severe that the animal scratches itself until it bleeds. Up to 15 per cent of animals with food hypersensitivity have accompanying gastrointestinal signs (vomiting and/or diarrhea). In both dogs and cats, the disease may be poorly responsive to glucocorticoids (steroids). The majority of dogs with food hypersensitivity manifest clinical signs before 3 years of age, but the disease may occur at any age.

The diagnosis of food allergy involves a food elimination trial. There is currently no other accurate test to determine whether your pet has food allergy. It is believed that animals may react to allergens in their food for up to 6 weeks or more; therefore a restrictive diet must be given for up to 10 weeks. Because food allergy is an acquired disease (a food component becomes allergenic after being fed), only foods that the animal has never eaten before may be used. One protein source and one carbohydrate source are chosen and all other foods are discontinued. Cats may eat a single protein source for the elimination trial. Your veterinarian will base the trial diet on what your pet has eaten in the past. Therefore, it is important to be complete when relating your animal's diet history.

During a food elimination trial, only that diet is fed. Treats, rawhide chews, dog biscuits, pig ears, chew hooves, vitamin pills, food supplements, or unapproved medications (including some heartworm preventives) should not be given. Your veterinarian may change the heartworm preventive that your pet is receiving to a nonflavored pill for the duration of the trial period. You may not use cheese, hot dogs, and so forth to disguise medication during the diet trial.

Treats must consist of the same ingredients used in the diet trial. Outdoor cats must be kept away from other food sources to have a successful food trial. It may be necessary to confine them indoors for the duration of the food trial.

Please exercise caution if you have other pets and make certain that the pet receiving the trial diet never has an opportunity to eat any of the other animals' food (or even lick their bowl). One morsel of another type of food has the potential to invalidate the entire elimination diet trial and could necessitate commencement of a different diet for 10 weeks. The other animals in the household could also be fed the elimination diet. Inform everyone in the household that your pet is receiving a special diet. It is important to be diligent when your pet is on walks to ensure that ingestion of foodstuffs does not occur. Simply changing the brand of dog food (even to diets that are described as "hypoallergenic") is not equivalent to an elimination diet. Most dog foods share similar protein, grain meal, preservatives, and/or dye sources and contain many potentially allergenic ingredients in order to be fully balanced. Your veterinarian will recommend a protein (e.g., fish, pork, tofu, lamb, pinto beans, rabbit, venison, duck) and a carbohydrate (e.g., potato, rice, oatmeal) in a ratio of one cooked pound of protein to six cups of cooked carbohydrate. Flavorings other than salt, pepper, and garlic may not be used (no oils, butters, or cooking spray). Many clients find it easier to prepare the diet in bulk (e.g., 1 week at a time) and freeze the diet in measured daily rations. Approximately one cup is fed per 10 pounds of body weight daily. Switch gradually to the new diet over a period of 3 to 5 days by giving more of the new diet and less of the old diet each day.

Some animals may have loose stools while receiving the trial diet. Your pet may develop vomiting, diarrhea, or constipation or may refuse to eat the new diet. Cats may begin to develop a serious liver disease if they do not eat for 2 days or more. Do not allow your eat to go without eating for more than 2 days, and consult your veterinarian if any of the other problems occur before giving up or changing the diet. Cats may be especially difficult to coax to eat the trial diet. If your veterinarian approves, certain baby foods may be used for cats for the elimination diet.

It is advisable to keep a daily diary during the trial so that progress may be monitored. Many clients use a calendar to record the level of itchy behavior (scale of 1 to 10) in conjunction with the body areas the pet is targeting. In the event that your pet refuses to eat the elimination diet, your veterinarian may recommend a commercial prescription limited-antigen diet. It is important that during the elimination diet no corticosteroids (pills, drops, or creams) are administered to your pet, as these drugs may cloud the assessment of the response to the trial diet.

The elimination diet is not a balanced diet and it is not recommended that pets continue to eat the diet for longer than 10 weeks without veterinary supervision. It is not necessary for your pet to exhibit 100 per cent improvement while receiving the diet; 50 per cent improvement may be sufficient to demonstrate response to the diet trial. It is important to remember that up to 30 per cent of food-hypersensitive dogs may exhibit multiple allergies (flea allergy, environmental allergies); therefore, the response to the diet may be partial. The confirmation of food hypersensitivity is definitively determined by dietary rechallenge. It is important to avoid changes in bathing, ear treatments, oral medications.

The original diet should be slowly reintroduced over 3 to 5 days and the pet monitored for increases in itching, which should return within 14 days. If the itching returns, stop feeding the original diet and revert back to feeding the elimination trial diet until your pet returns to normal. If your pet is diagnosed with food hypersensitivity, your veterinarian will work closely with you to try to select a commercial diet that contains ingredients to which your pet is not allergic. In rare instances, pets may react to all commercial diets and must receive a home-cooked diet. Your veterinarian may consult veterinary nutritional specialists (usually located at veterinary colleges) who can provide a recipe that completely balances the home-cooked diet.

The above is general veterinary information. Do not begin any course of treatment without consulting your regular veterinarian. All animals should be examined at least once every 12 months.

About the author:

From the Textbook of Veterinary Internal Information: Client Information Series. Copyright © 2000 by W.B. Saunders Company. All rights reserved.

Linda Mar Veterinary Hospital and its cat-only affiliate, Coastal Cat Clinic, are small animal practices located in Pacifica, California.

 Terese C. DeManuelle, DVM